International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is the mass of a neutron, typically measured in atomic mass units?

1. 1

2. 0

3. 1.008

4. 1.007

The correct answer is: 1

The mass of a neutron is approximately 1 atomic mass unit (amu). In atomic mass units, the neutron is often rounded to exactly 1 amu for simplicity, even though its precise mass is slightly higher than that (approximately 1.008665 amu). This close approximation is significant because atomic mass units provide a way to compare the relative masses of subatomic particles conveniently. In practical applications and when teaching basic concepts, it’s common to refer to the neutron's mass as "1 amu” since this aids in understanding the overall mass of atoms, where protons and neutrons contribute significantly to the nuclear mass. By convention, the mass of protons and neutrons is similar enough that their masses are often rounded for ease of calculations and discussions about atomic structures. The other choices do not accurately represent the mass of a neutron in atomic mass units.